Combined chloroquine and ribavirin treatment does not prevent death in a hamster model of Nipah and Hendra virus infection.

Abstract

Hendra virus (HeV) and Nipah virus (NiV) are recently emerged, closely related and highly pathogenic paramyxoviruses that cause severe disease such as encephalitis in animals and humans with fatality rates of up to 75 %. Due to their high case fatality rate following human infection and because of the lack of effective vaccines or therapy, they are classified as Biosafety Level 4 pathogens. A recent study reported that chloroquine, an anti-malarial drug, was effective in preventing NiV and HeV infection in cell culture experiments. In the present study, the antiviral efficacy of chloroquine was analysed, individually and in combination with ribavirin, in the treatment of NiV and HeV infection in in vivo experiments, using a golden hamster model. Although the results confirmed the strong antiviral activity of both drugs in inhibiting viral spread in vitro, they did not prove to be protective in the in vivo model. Ribavirin delayed death from viral disease in NiV-infected hamsters by approximately 5 days, but no significant effect in HeV-infected hamsters was observed. Chloroquine did not protect hamsters when administered either individually or in combination with ribavirin, the latter indicating the lack of a favourable drug-drug interaction.

Dose–response curves for chloroquine (a) and ribavirin (b). HeLa cells were infected with 103 TCID50 HeV and fresh medium containing serial twofold dilutions of ribavirin or chloroquine were added at 1 h pi. Cells were incubated for 24 h prior to harvesting of the cell supernatants for titration in Vero cells. Non-linear regression analysis was performed using SigmaPlot software to determine IC50. Values are expressed as the mean log drug concentration and plotted against infectious HeV titres±sem (n=3). The continuous line represents a non-linear sigmoidal fit.

Prophylactic effect of chloroquine. HeLa cells were pre-treated with 20 μM chloroquine (a) or 100 μM ribavirin (b) for 12 h prior to virus infection, or the drugs were added at the time of infection (0 h) or at the times indicated. Cells were infected with 103 TCID50 HeV. At 1 h p.i., cells were washed with DMEM and fresh medium was added. Pre-treated cells were maintained in the absence of drugs, whilst for the other time points, the medium contained 20 μM chloroquine or 100 μM ribavirin. Cells were incubated for 24 h prior to harvesting of the cell supernatants for titration in Vero cells. Results are shown as means±sem (n=3).

Effects of ribavirin and chloroquine on the survival of NiV- and HeV-infected hamsters. Animals were infected by the i.p. route with 104 TCID50 NiV (a) or HeV (b) in 100 μl. At 6 h p.i., treatment was initiated by dosing with 30 mg ribavirin kg−1 twice daily (○), 50 mg chloroquine kg−1 every other day (▾) or a combination of both drugs (▵). Infected control animals received vehicle solution only (•).

Effect of body weight on the sensitivity to NiV or HeV infection in hamsters. Change in body weight (g) of NiV-infected control animals (a) and HeV-infected animals (b) over the course of the experiment. The numbers on the graph indicate the animal number referred to in Results.